This invention relates to a semiconductor ROM (read only memory).
In the past, circuits have been developed which correct erroneous data read out from a defective memory cell, by the use of, e.g., the Hamming code or the cyclic code (hereinbelow, termed "ECC (error correcting code) circuit").
The inventors studied building an ECC circuit in a semiconductor ROM to the end of correcting erroneous data read out from a defective memory cell in the semiconductor ROM. However, when the ECC circuit is provided within the semiconductor ROM, the error correcting operation renders the read-out access time of the ROM long and the operating speed thereof much lower. Moreover, a memory array must be provided with memory cells for redundant bits, and the arrangement of the ECC circuit is complicated, resulting in the disadvantage that the chip size of the semiconductor ROM becomes large.